predicting power consumption

[Nyper]

In planning a rack, how do you accurately predict the amperage that the rack will consume?

For instance, we have a rack with 19 pieces of equipment in it that is consuming approximately 22amps. How can we predict how many more amps will be consumped by adding a new piece of equipment?

Example - a Dell Poweredge 2850 has a max of 700 watts, which is about 6.4 amps on a 110v circuit, correct? Obviously it wont pull the whole 700 watts and won't use a full 6.4 amps. How can I predict what we need?

Another example - we have a load balancer that pulls a max of 90 watts. This is about the equivalent of 0.8 amps on a 110v circuit. Yet, the specs in the manual say the switch has a 3amp fuse. How the heck can I predict how many amps will be used?

 

[dedub]

Nyper, Your Math is correct. For others..... take the wattage and divide by the voltage eg.. 700w/110v = 6.36 Amps. I believe you are tracking on everything else. That 2850 rated for 700w is the Max it will ever pull, normally during boot. Same with all other equipment. The only way to see what it is pulling during normal Op. is to use an Amp meter inline with the power cord. Plus, Manufacturers always put fudge in thier rating to save themself lawsuits.... Blown UPS ect....
Now as far as the load balancer I'm confused, Im not sure where that fits into your power scheme.
Lastly, you never want to power everything up at the same time. That's where you can spike your consuption and pop breakers/ blow fuses.

 

[Nyper]

My problem is finding/making an affordable in-line amp meter that can be used for individual appliances. I'm thinking I may have to rig up somethign use an extension cord with the sheathing stripped away.

 

[dedub]

Darn, I thought I had that idea pattened No really, I did the same thing with a radio shack $20.00 model. Works fine! My 'Pigtail' is about 6" long. I stripped about 3 inches away from one of the wires so they WILL NOT touch and put some heavy aligator clips on the meter.
good luck